The molecular mechanism by which glucose and other fuels stimulate insulin release is still uncertain. ?-Cells possess a unique stimulus-response coupling system which requires that the fuel stimulus be metabolized to initiate membrane electrical events then secretion. Exposure of pancreatic ? cells to stimulatory concentrations of glucose is known to decrease the activity of the KATP-channels. This results in depolarization of the membrane potential, Ca2+-dependent bursting electrical activity and insulin secretion. It is clear that fuel-induced secretion, likeother secretory processes, is mediated in part by elevations in cytosolic free Ca2+. Although it is hypothesized that changes in metabolism precede changes in Ca2+, this has never been documented at the single cell level. Single cell Ca2+ studies have been published extensively and it is well-established that oscillations in Ca2+ occur in response to glucose stimulation. However, the pattern observed in single cells (mostly oscillatory) is quite different from the pattern obtained in cell suspensions (monophasic). The present studies were undertaken to evaluate whether the pattern of O2 consumption in single ?-cells supported a model in which metabolic oscillations preceded and caused oscillatory changes in Ca2+. A second goal was to determine the percentage of responding cells and whether increasing glucose concentrations increased O2 consumption in each cell or recruited previously unresponsive cells, as has been hypothesized for Ca2+. The results of these studies showed tha t oscillations in O2 consumption occurred in the basal state and increased in amplitude in response to stimulation by glucose (15 mM). These oscillations were blocked by uncoupling respiration with the chemical uncoupler, FCCP, which stimulated O2 consumption. They were also blocked and respiration totally inhibited by antimycin A, a bc1 complex inhibitor. The question of whether Ca2+ modulated the oscillations in O2 and, indeed, whether the O2 oscillations were independent of Ca2+, was addressed by monitoring O2 in the absence of added Ca2+. Oscillations in O2 occurred inthe absence of Ca2+, increased in response to stimulatory glucose and increased still further in response to restoration of a normal extracellular Ca2+ level. In the presence of normal extracellular Ca2+, basal O2 oscillations were greater and increased still further in response to glucose. These studies indicate that the O2 oscillations did not require Ca2+ but that the amplitude of the O2 oscillations were much greater under conditions where insulin secretion was stimulated. When studying the response of cell to maximal stimulation by glucose most cells exhibited basal oscillations in O2 consumption and that about half of the cells responded with a marked increase in the amplitude of oscillations while the remainder did not respond at all. The data obtained also al lowed analysis of the amplitude and period of oscillations in O2 consumption from two different clonal ?-cell lines. In order to determine how the cells responded to substimulatory concentrations of glucose experiments were performed in which O2 consumption was monitored in multiple cells following addition of two consecutive submaximal additions of glucose. It was determined that cells exhibited and all or none response with no evidence of a concentration dependence.